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Creating Cut-Away Images with Cutting Planes

Cutting planes provide slices of your data...slicing the data as if with a knife. With cutting planes, you can investigate response values visually slice by slice, as you increment, decrement, or randomly select a position. The face of each slice is colored according to the response values. SAS/SPECTRAVIEW provides:

• three axis cutting planes that cut perpendicular to the X, Y, or Z axis, which display in the Volume window. In addition, you can display two- and three-dimensional surface views of the data (such as surfaces, charts, and plots), showing the values at each location along the specified axis, which display in the surface windows.

• one NOR cutting plane (non-orthogonal), meaning that the plane is not perpendicular to any axis, which displays in the Volume window.

Displaying an Axis Cutting Plane

The three axis cutting planes cut perpendicular to the X, Y, or Z axis. For example, the Y cutting plane lies parallel to the XZ plane and perpendicular to the Y axis. An axis cutting plane can be displayed in either block contour format (solid-block) or line contour format (continuous lines). To display an axis cutting plane in the Volume window:

1. Select [Tools], then [Planes].

   The three axis cutting planes are labeled with the variable names you specified for the X, Y, and Z axes. For example, using the MORTGAGE data set and specifying RATE as the X variable, AMOUNT as the Y variable, and YEARS as the Z variable, results in the axis cutting planes:

   • [YEARS Plane =>]

   • [AMOUNT Plane =>]

   • [RATE Plane =>]

   The labels for the axis cutting planes also contain a => symbol indicating that the button is a pull-down button, which means that pressing the button will display a menu of choices.

2. Position the cursor on the pull-down button representing the axis cutting plane you want to display, then press and hold down the left mouse button to display a menu of choices. The additional buttons are displayed only while you press the mouse button.

   Pull-Down Buttons for Axis Cutting Planes
   

   

   The top choices represent how the cutting plane will be displayed in the Volume window (as solid blocks or line contours), and the bottom choices control which type of image appears in the surface window.

3. Drag the mouse to one of the following choices, then release the mouse to select it:

   [Block contour w/]

   to display the cutting plane in a solid-block format. Note that for sparse data, a block-contour image may appear as separate blocks, because each block represents one data point in the current plane.

   [Line contour w/]

   to display the cutting plane as continuous lines. Note that a line-contour image needs at least four data points at each grid intersection to be displayed, which may not exist for sparse data.

   [Off]

   to turn off the displayed cutting plane.

In the following example, which uses the MORTGAGE data set, the response values (for PAYMENT) are displayed against the Z cutting plane by selecting [YEARS Plane=>] then [Block contour w/]. The cutting plane shows the impact of varying interest rate and loan amounts for a given year. That is, the year is held constant and the impact of the other two variables on the payment amount is shown. You can move the cutting plane over the range of years to examine other combinations based on a given year value.

Y-Axis Cutting Plane

Including Surface Views for an Axis Cutting Plane

You can display two- and three-dimensional surface views of data, such as surfaces, charts, stacks, and plots. The surface views represent the data at a selected cutting plane's current location, and they display in an appropriate surface window. To request a surface view:

1. Select [Tools], then [Planes].

   The three axis cutting planes are labeled with the variable names you specified for the X, Y, and Z axes. For example, for the MORTGAGE data set, RATE is the X variable, AMOUNT is the Y variable, and YEARS is the Z variable, which results in the axis cutting planes

   • [YEARS Plane =>]

   • [AMOUNT Plane =>]

   • [RATE Plane =>]

   The labels for the axis cutting planes also contain a => symbol indicating that the button is a pull-down button, which means that pressing it will display a menu of choices.

2. Position the cursor on the pull-down button representing the axis cutting plane you want to display, then press and hold down the left mouse button to display a menu of choices. The additional buttons are displayed only while you press the mouse button.

   Pull-Down Buttons for Surface Views
   

   

   The top choices represent how the cutting plane will be displayed in the Volume window (as solid blocks or line contours), and the bottom choices control what type of image appears in the surface window.

3. Drag the mouse to one of the following choices, then release the mouse to select it:

   [3D surface]	to create a three-dimensional surface of the axis cutting plane. The third dimension is response.
   [3D chart]	to create a three-dimensional chart of the axis cutting plane. The third dimension is response.
   [3D stack]	to create a three-dimensional stacked line contour of the axis cutting plane. The third dimension is response.

   For the respective axes:

   [axis chart]	to create a two-dimensional bar chart of the responses across all values of the axis. For example, for the X cutting plane, selecting the Z chart produces a color chart of the responses across all values of Z at the current X location of the cutting plane. The Y value remains constant at its current value.
   [axis plot]	to create a two-dimensional plot of the response values across all values of the axis. For example, for the X cutting plane, selecting the Z plot produces a color plot of the responses across all values of Z at the current X location of the cutting plane. The Y value remains constant at its current value.

   The image displays in the appropriate surface window in solid-block format. That is, a surface view of a cutting plane along the Z axis displays in the XY Surface window, a cutting plane along the Y axis displays in the XZ Surface window, and a cutting plane along the X axis displays in the YZ Surface window. Note that when you request a surface view, if its associated axis cutting plane is not already displayed, it automatically displays in the Volume window.

In the following example, a three-dimensional chart is displayed in the XY Surface window by selecting [YEARS Plane=>] (Z cutting plane), then [3D chart]. The chart is linked to the Z cutting plane's current position.

Three-Dimensional Chart in XY Surface Window

Displaying a NOR Cutting Plane

The NOR cutting plane (non-orthogonal) is not perpendicular to any axis. You can use the NOR cutting plane to cut the data in any manner you wish. It displays in block contour only. To display the NOR cutting plane in the Volume window:

1. Select [Tools], then [Planes].

   The labels for the cutting plane buttons contain a => symbol indicating that the button is a pull-down button, which means that pressing it will display a menu of choices.

2. Position the cursor on the [NOR plane =>] pull-down button, then press and hold down the left mouse button to display a menu of choices. The additional buttons are displayed only while you press the mouse button.

3. Drag the mouse and select [Block contour] to display the cutting plane in a solid-block format. (Selecting [Off] turns off the displayed cutting plane.)

In the following example, using the MORTGAGE data set, the NOR cutting plane is displayed along with the Y cutting plane.

NOR Cutting Plane

Moving a Cutting Plane

The initial position of a cutting plane shows a section at the minimum value for the axis. Moving a cutting plane lets you view the data slice by slice, allowing you to position a cutting plane at a specific location along the axis.

As you move a cutting plane, the data at the various locations along the axis displays against the cutting plane and in any two- or three-dimensional surface views. If there is no data for the cutting plane's current location, the cutting plane will not display, unless you have assigned color to missing values.

• To automatically move a displayed cutting plane continuously along its axis, select [Auto]. The response values display against the cutting plane as it moves through the volume grid, stopping at each unique value for the axis. Only one plane at a time can move continuously. (To make the plane stop moving, click the left mouse button.)

• To manually move a cutting plane to a specific point on the axis by stepping it through the data incrementally, use the [-] (backward) and [+] (forward) buttons.

  Or, select the [Xform] global button, select either [Move plane] (for the axis cutting planes) or [NOR rotate] (for the NOR cutting plane), drag the cursor along the axis to the appropriate point, and release the mouse button.

Moved Cutting Plane

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Copyright 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.